This invention relates generally to forms for concrete structures, and particularly those kinds of structures in which an interior face or faces are formed, commonly known as core-walls, for the construction of elevator shafts, stairwells, tunnels, culverts and similar structures in which an interior space is desired.
These and other concrete structures are normally formed by the use of prefabricated forming systems that are assembled into modular or gang forms by means of appropriate connecting hardware such as gang rods and bolts etc. The assembled ganged form is then crane handled into a final concrete pouring position. In the case of forming core-walls, an outside form is also assembled to thereby create a median space between the inner core form and the outer form, which space then receives the wet concrete. Removal or stripping of the core-wall form from the concrete, once the latter has set, has been done in the past by using hinge assemblies located at each corner of the form, as well as at locations generally midway between the corners of the form, so that the entire form is made to collapse inwardly and thereby allow its subsequent removal from the concrete core or shaft.
More recently such articulated collapsible forms have been designed with fixed sides and end walls having only a hinge assembly at each corner of the form, such as shown in U.S. Pat. No. 4,055,321. In this way, the rigidity of the form structure is somewhat enhanced and therefore not entirely sacrificed at the expense of articulated collapsibility, it being understood that a foremost criterion is that the form itself should preferably present a smooth and rigid surface to the wet concrete.
Lessening the number of joints or hinges in the form structure is, of course, a desirable end in itself, and the present state of the art does reflect the direction taken towards this end. However, there still remains much room for improvement if an ideal form structure for forming smooth concrete core wall surfaces is to be realized in which such a form, (1) presents a smooth surface to the wet concrete, (2) uses a minimum number of joints and hinges, (3) minimizes the time required to activate the hinges and hinge related structures and joints to thus stip the form from the concrete, and (4) offers a rigid structure to the cement in the setting stage, especially at the corners which must be maintained at 90.degree. for acceptable rectangular or square configurations of the finished core shaft.